1. Field of the Invention
The present invention relates to a magnetic detector for detecting, e.g., a rotational angle of a gear-like rotary member of magnetic material, and more particularly to a magnetic detector for detecting, e.g., rotation information of an internal combustion engine.
2. Description of the Related Art
FIG. 15 is a side view of a conventional magnetic detector, FIG. 16 is a side sectional view thereof, and FIG. 17 is a schematic view of a magnetic circuit incorporated in the magnetic detector.
A detector body 1 comprises a cylindrical case 3 made of a synthetic resin, an electric circuit unit 4 housed in the case 3, a parallelepiped magnet 5 provided at a fore end of the electric circuit unit 4, and a detecting unit 6 provided in a front surface of the magnet 5 and including a magnetic field sensing device built therein.
In such a magnetic detector, when a gear-like rotary member of magnetic material 21 provided close to the magnetic detector is rotated, a recessed portion 21a and a projected portion 21b of the rotary member of magnetic material 21 alternately approaches the detecting unit 6, whereupon a magnetic field applied from the magnet 5 to the detecting unit 6 is changed. Changes in the applied magnetic field are detected as voltage changes by the detecting unit 6. The voltage changes are output to the external in the form of a pulse-wave electric signal through a differential amplification circuit, a comparison circuit and an output circuit in the detecting unit 6. The electric signal is sent through a terminal of a connector 2 to a computer unit (not shown) which processes the electric signal to detect a rotational angle of the rotary member of magnetic material 21.
A magnetoresistive device (referred to as MR device hereinafter) or a gigantic magnetoresistive device (referred to as GMR device hereinafter) is employed as the magnetic field sensing device.
The MR device is a device of which resistance value varies depending on an angle formed between the magnetized direction and the current direction in a thin film of a ferromagnetic material (e.g., Nixe2x80x94Fe or Nixe2x80x94Co). The MR device has a minimum resistance value when the current direction and the magnetized direction cross at a right angle, and a maximum resistance value when the current direction and the magnetized direction cross at 0 degree, i.e., when the two directions are the same or exactly opposed to each other. Such a change in resistance value is called an MR change rate and generally ranges 2-3% for Nixe2x80x94Fe and 5-6% for Nixe2x80x94Co.
A GMR device is a so-called artificial lattice film, i.e., a laminate manufactured by alternately forming a magnetic layer and a non-magnetic layer with thicknesses of several angstroms to several tens of angstroms one on top of the other as described in xe2x80x9cMagnetoresistance Effect of Artificial Latticexe2x80x9d, Journal of the Applied Magnetism Society of Japan, Vol. 15, No. 51991, pp. 813-821. Such known artificial lattice films are represented by (Fe/Cr), (Permalloy/Cu/Co/Cu), and (Co/Cu). The GMR device exhibits a much greater MR effect (MR change rate) than the above-mentioned MR device. Also, the GMR device is a so-called in-plane magnetic sensitive device which produces the same resistance changes regardless of any angular difference in direction of an external magnetic field with respect to a current. Generally, the GMR device has an MR change rate of about 20-30%.
The magnetic detector operates exactly in the same manner in both cases of using the MR device and the GMR device; hence the operation in the case of using the MR device will be described below in detail.
When the rotary member of magnetic material 21 rotates, the magnetic field applied to the MR device is changed and a resistance value of the MR device is also changed. For detecting changes in magnetic field, it is conceivable to form a bridge circuit with MR devices, connect a constant-voltage and constant-current power supply to the bridge circuit, and convert changes in resistance values of the MR devices into voltage changes, thereby detecting changes in the magnetic field acting on the MR devices.
FIG. 18 is an electric circuit diagram of the conventional magnetic detector using MR devices.
The electric circuit of the conventional magnetic detector comprises a bridge circuit 11 using MR devices, a differential amplification circuit 12 for amplifying an output of the bridge circuit 11, a comparison circuit 13 for comparing an output of the differential amplification circuit 12 with a reference value and outputting a signal having a level of xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d, and an output circuit 14 for receiving an output of the comparison circuit 13 and shaping an output signal through switching operation.
The bridge circuit 11 includes MR devices A and B. The MR device A is connected at one terminal to a power source terminal Vcc, and the MR device B is grounded at one terminal. The other terminals of the MR devices A and B are connected to a junction point A. Then, the junction point A of the bridge circuit 11 is connected to an inverted input terminal of an amplifier in the differential amplification circuit 12.
A non-inverted input terminal of the amplifier is connected through a resistor to a voltage dividing circuit which constitutes a reference power supply, and then grounded through a resistor. An output terminal of the amplifier is connected to the inverted input terminal thereof through a resistor, and also to an inverted input terminal of an amplifier in the comparison circuit 13. A non-inverted input terminal of the amplifier in the comparison circuit 13 is connected to a voltage dividing circuit which constitutes a reference power supply, and also to an output terminal thereof through a resistor. An output terminal of the amplifier in the comparison circuit 13 is connected to the power source terminal Vcc through a resistor, and also to a base of a transistor in the output circuit 14. A collector of the transistor is connected to an output terminal and also to the power source terminal vcc through a resistor, whereas an emitter of the transistor is grounded.
FIG. 19 is a waveform chart showing the waveform processing operation of the conventional magnetic detector.
Upon rotation of the rotary member of magnetic material 21, the MR devices are subject to changes in magnetic field and the differential amplification circuit 12 produces an output, shown in FIG. 19B, that varies corresponding to the alternately projected and recessed portions of the rotary member of magnetic material 21 shown in FIG. 19A. The output of the differential amplification circuit 12 is supplied to the comparison circuit 13 and compared with a reference value, i.e., a comparison level, set in the comparison circuit 13 for conversion into a signal having a level of xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d. This signal is then shaped in waveform by the output circuit 14. As a result, an output having steep rising and lowering edges and a level of xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d, shown in FIG. 19C, is produced at the output terminal of the output circuit 14.
Generally, a computer unit used in controllers for internal combustion engines, for example, receives an output signal from a detector and controls equipment based on the received signal. The higher resolution of the output signal, the higher accuracy can be provided by the computer unit in control. A demand for higher accuracy in control is often critical in the art.
With the conventional magnetic detector, however, pulses are output just in the same number as the projected or recessed portions of the rotary member of magnetic material, and an output signal with higher resolution cannot be produced. There has been thus a problem that highly accurate control cannot achieved when the conventional magnetic detector is used as detecting means in, e.g., controllers for internal combustion engines.
With a view of solving the problem described above, an object of the present invention is to provide a magnetic detector which can output pulses as many as twice the number of projected or recessed portions of a rotary member of magnetic material.
A magnetic detector according to a first aspect of the present invention comprises a magnetic field generating means for generating a magnetic field, a moving member of magnetic material disposed with a predetermined gap retaining relative to the magnetic field generating means and being able to change the magnetic field generated by the magnetic field generating means, and an in-plane-sensitive magnetic field sensing device for detecting changes in the magnetic field by movement of the moving member of magnetic material, wherein the magnetic field sensing device is arranged in a region where a magnetic field acting on the magnetic field sensing device changes from positive to negative and from negative to positive with the movement of the moving member of magnetic material.
In a magnetic detector according to a second aspect of the present invention, in addition to the features of the first aspect, the magnetic field sensing device is arranged to have a magnetic sensitive surface lying vertically to the magnetized direction of the magnetic field generating means which is magnetized in a direction opposing to the moving member of magnetic material, and first center axes of the magnetic field sensing device and the magnetic field generating means are substantially aligned with each other.
In a magnetic detector according to a third aspect of the present invention, in addition to the features of the second aspect, the magnetic field sensing device is arranged between the magnetic field generating means and the moving member of magnetic material in sandwiched relation.
In a magnetic detector according to a fourth aspect of the present invention, in addition to the features of the first aspect, the magnetic field sensing device is arranged to have a magnetic sensitive surface disposed in a first surface of the magnetic field generating means which is magnetized in a direction opposing to the moving member of magnetic material, and first center axes of the magnetic field sensing device and the magnetic field generating means are substantially aligned with each other.
In a magnetic detector according to an fifth aspect of the present invention, in addition to the features of the fourth aspect, the magnetic field sensing device is arranged to have a second center axis substantially aligned with an end surface of the magnetic field generating means which is opposed to the moving member of magnetic material.
In a magnetic detector according to a sixth aspect of the present invention, in addition to the features of the first aspect, a gigantic magnetoresistive device is used as the magnetic field sensing device.
In a magnetic detector according to a seventh aspect of the present invention, in addition to the features of the first aspect, the detector includes a bridge circuit comprising a plurality of magnetic field sensing devices, and at least one of the plurality of magnetic field sensing devices is arranged in a region where resistance changes are saturated.
In a magnetic detector according to an eighth aspect of the present invention, in addition to the features of the seventh aspect, the magnetic field sensing device, which is arranged in the region where resistance changes are saturated, is disposed side by side with respect to another magnetic field sensing device.
In a magnetic detector according to a ninth aspect of the present invention, in addition to the features of the first aspect, the detector includes a bridge circuit comprising at least two magnetic field sensing devices each having anisotropy, one of the two magnetic field sensing devices is arranged to have a magnetism sensing direction coincident with the moving direction of the moving member of magnetic material, and the other of the two magnetic field sensing devices is arranged to have a non-magnetism sensing direction coincident with the moving direction of the moving member of magnetic material.